A thickener or other apparatus may be used in the field of gravity-driven separation of a solid-liquid mixture (a viscous material) into clarified liquid and concentrated solids. Feed may enter a thickener in a feedwell, for example, at the center of the thickener where a reagent (e.g., a flocculant) is added to enhance separation. In steady state operation of such a thickener, three distinct zones are formed with the processed viscous material. The upper zone contains clarified liquid. Below that is a settling zone where solid particles are moving generally downward while liquid is moving generally upward. The lowest is the compaction zone. Usually the interface between the settling zone and compaction zone is quite distinct, having different physical properties.
There have been several methods introduced in the industry to locate this interface, or bed location, within the thickener. These methods include ultrasonic sensors mounted on the bridge and a differential pressure sensor mounted on the bottom of the tank. These methods infer the bed location indirectly rather than directly. Further, consistent identification of the bed level on a continuous basis in the dynamic thickening process has proven difficult using these methods. In addition, the effectiveness of the flocculants, which are often used in thickeners, results in evolving density gradients clouding the interface and creating a fluffy bed, which often results in bed level measurement errors.
Another method employed in the industry mechanically lowers a conductivity sensor down from the bridge into the thickener, measuring the conductivity profile as it is lowered. The expense of this method and the chance of entanglement with a raking mechanism, which is often used in a thickener, are additional drawbacks for this method. Further, this method does not continuously obtain data regarding the state of the viscous material within the thickener.
Furthermore, problems can arise in the thickener because of variations in the horizontal gradient of the viscous material. Without this knowledge, an operator of the thickener may improperly add or reduce, for example, flocculant to the viscous material, potentially exacerbating the problem.
Accordingly, an improved apparatus for ascertaining an interface between the compaction zone and the settling zone in a viscous material within a thickener is desirable. An improved apparatus for ascertaining the horizontal viscosity characteristics of a viscous material within a thickener is also desirable.